Turbochargers can have a turbine wheel that is connected by a shaft to a compressor wheel. The turbine wheel is driven by exhaust gas exiting an internal combustion engine. The rotation of the turbine wheel is communicated to the compressor wheel by the shaft. The compressor wheel is used to increase the pressure of intake air prior to mixing with fuel and combustion in the engine. The speeds at which the shaft, turbine wheel and compressor wheel are rotated is very high, and can be in excess of 60,000 rpm including up to or above 300,000 rpm. Bearings used to support the shaft therefore must be lubricated with pressurized oil. During normal operation of the turbocharger, pressure within the compressor is sufficient to retard the flow of oil from the area of the bearings into the compressor. During certain operational states, pressure is reduced in the compressor and a pressurized oil can be drawn into the compressor area where the oil will contaminate the intake air. Such contaminated air is burned in the engine, generating undesired emissions and potentially damaging certain downstream components. It is therefore necessary to provide appropriate sealing structure to prevent the flow of pressurized oil into the compressor.
There is shown in FIG. 1 a prior art system in which a turbocharger 10 includes a turbine wheel 14, a compressor wheel 18, and a connecting shaft 22. A first bearing 26 and a second bearing 28 can be provided to support the shaft 22. An oil intake 30 communicates with oil passages 34, 38 to deliver oil to the first bearing 26 and the second bearing 28. Additionally, a thrust collar 40 is fixed to and rotates with the shaft 22. The thrust collar 40 includes a first radially outwardly extending wall 44 and a second radially outwardly extending wall 48 (FIG. 2). A thrust bearing 50 has a radially inner end 54 that rests in an annular channel formed by the first radially outwardly extending wall 44 and second radially outwardly extending wall 48 of the thrust collar 40. The thrust bearing 50 controls axially directed movement of the shaft 22.
Lubrication is provided by oil passageway 60 which receives oil from the oil intake 30. Oil escaping from the interface between the first radially outwardly extending wall 44 and the thrust bearing 50 is prevented from reaching the compressor wheel 18 by the provision of a seal assembly including an oil deflector 64 and an insert 68. The deflector 64 has an irregular form to facilitate the drainage of oil. Oil passing the deflector 64 is contacted by an oil thrower 72. The oil thrower 72 is connected to the shaft 22 and rotates therewith. Oil is thrown by the thrower 72 into the chamber 76 where it contacts a deflecting surface 80. The deflecting surface 80 collects the oil and the oil flows gravitationally to the outlet 84. Notwithstanding the presence of the insert 68, oil can flow past the interstices between the insert 68 and the oil thrower 72 to reach the compressor wheel 18. Further, the configuration does not reliably drain oil from the chamber 76.
In U.S. Pat. No. 6,338,614 to LaRue, an annular gland seal is described which attempts to control axially directed thrust imposed on the shaft from the turbine housing shaft end while also attempting to provide a seal between the gland seal and the housing. As shown in FIGS. 3 and 4, the LaRue gland seal 110 has a body 112 having a hollow shaft passage 114 extending axially therethrough from a first body end 116 to a second body end 118. The gland body 112 includes a first diameter section 120 that extends axially a distance away from the first end 116 to a groove 122. The groove 122 is sized and designed to accommodate placement of an annular sealing ring. A second diameter section 124 extends axially from the groove 122 to a shoulder 126 that projects radially outwardly away from the second diameter section.
The shoulder 126 is sized and positioned to interact with an axially projecting section of the compressor backplate. The body 112 includes a flange 128 that is directed radially outwardly away from the shoulder 126 and that is configured to facilitate the passage of oil therethrough via a plurality of radial oil pumping holes 130. The holes 130 are defined axially by a first axial flange surface 132 and an oppositely facing second axial flange surface 134. A third diameter section 136 extends axially from the flange 128 and has a diameter that is greater than both the first and second diameter sections. The third diameter section 126 extends axially to a radially inwardly directed section 138 that is sized to cooperate with a housing member or bearing element within the turbocharger center housing. A fourth diameter section 140 extends axially from the radially inwardly direction section 138 to a radially outwardly flared section 142. The gland body flange 128 and/or radially outwardly flared section 140 are intended to control axially-directed thrust loads that are imposed on the gland by the shaft.
The drawback of the LaRue design is that the flange portion 128 abuts the compressor back plate, but oil is directly supplied via oil pumping holes 130 to the axially projecting section of the backplate that is inserted into shoulder 126. The radially inner portion of oil pumping holes 130 rests directly upon the compressor back plate projection and provides direct access to shoulder 126. As such, the oil is in close proximity to the interstices between the backplate projection and the shoulder 126. This proximity increases the likelihood that the oil will escape through the shoulder 126 and into the compressor.
In U.S. Pat. No. 4,420,160 to Laham, a face seal system is described which attempts to provide a seal between the compressor housing and shaft through use of a biasing mechanism. Referring to FIG. 5, the Laham face seal system 250 has a spring 262 in a recess within the backplate 228 that opens axially toward the interior of the center housing. The recess has an annular flange 266 formed concentrically about and slightly spaced with respect to a spacer 246, and extending axially into the center housing toward a thrust collar 245. The backplate 228 has a plurality of anti-rotation lugs 270 projecting radially inwardly into the recess to form a relatively small annular undercut 271 for reception and positioning of the seal system 250.
A thrust washer 268 has along its periphery a plurality of slots circumferentially arranged for registry with the anti-rotation lugs 270. The spring 262 biases the thrust washer 268 into axial engagement with the anti-rotation lugs 270. A seal member 274 has a plurality of slots 276 configured for registry with the anti-rotation lugs 270. The seal member 274 has an axially presented seal face 278 for bearing and sealing engagement with the rotating thrust collar 245 mounted on the shaft 216 of compressor impeller 212. The seal member 274 also has an opposite axially presented face 279 for bearing engagement with the thrust washer 268. The axial length of the seal member 274 is chosen such that the spring 262 urges the thrust washer 268 into engagement with the face 279 of the seal member 274, which correspondingly urges the sealing face 278 of the seal member 274 into sealing engagement with the thrust collar 245.
An annular resilient seal ring is interposed radially between the backplate flange 266 and the seal member 274 to seal against passage of fluids therebetween. The seal ring is axially positioned between the thrust washer 268 and a radially stepped shoulder formed on the inner diameter of the seal member 274. The thrust washer 268 and the seal ring purportedly combine to adjust the sealing force between the seal face 278 and the thrust collar 245.
The drawback of the Laham design is that the seal member 274 is positioned radially inward of the thrust collar 245 in the region of seal face 278. This positioning creates a reservoir for oil to be in close proximity to any interstices along seal face 278. This proximity increases the likelihood that the oil will escape through the seal face 278 and into the compressor. Additionally, the seal face system 250 relies upon biasing of the seal member 274 against the thrust collar 245. Such an arrangement of face seal system 250 adds cost and is prone to failure over time, especially in the harsh environment of a turbocharger.
Other arrangements have also been used for sealing that suffer from similar drawbacks. In U.S. Pat. No. 5,890,881 to Adeff, additional components at added cost are incorporated into the sealing design in the form of a collar, a ring and a positive face seal. However, the Adeff design positions the positive face seal essentially flush with the ring in the region of the seal face. This arrangement creates a reservoir for oil to be in close proximity to any interstices along the seal face and increases the likelihood that the oil will escape through the seal face and into the compressor.
Thus, there is a need for a turbocharger with an oil discharge or seal assembly that can reduce or eliminate oil leakage. There is a further need for such an assembly and turbocharger that can do so while minimizing complexity and/or cost. There is yet a further need for such an assembly and turbocharger that maintains reliability.